1. Field of the Invention
The present invention relates to a sound processing method and apparatus for performing predetermined sound processing such as sound field control, sound quality control and interval control on an input audio signal to obtain a desired audio signal, and more particularly to a sound processing method and apparatus especially suitable for sound processing of audio signals containing sounds from a plurality of sound generating sources.
2. Prior Art
In a conventional sound processing apparatus, an input audio signal of one system is assumed to be a sound source signal of one system, and desired sound processing is performed on this input signal according to predetermined processing steps. This will be explained in detail by referring to a conventional sound field addition apparatus as shown in FIG. 7. In the apparatus shown in FIG. 7, a sound field control operation is performed on audio signals XL, XR that are input as a 2-channel stereophonic signal by sound field controllers 101a, 101b with a sound field control function f(X). The sound field-controlled signals fXL, fXR are output-controlled by an output controller 102 to be output as output audio signals YL, YR.
Another known example of sound field control processing system is disclosed by Japanese Patent Publication (Kokoku) No. 7-44759, in which sound field control is performed on a sum signal and a difference signal which are generated from a 2-channel stereophonic signal as an input signal.
However, no sound processing apparatus has ever been known in which an input audio signal is first separated into a plurality of separated signal components, which are then subjected to preliminary processing, and independent sound processing is performed on each of these signal components. Thus, it has been very difficult to selectively enhance or suppress individual sound source signals contained in the input audio signal to create a natural spatial impression of sound with a presence.
For example, in a sound field addition apparatus for adding a hall sound field to an input audio signal, it is basically assumed that a single sound source exists only on a stage. Addition of initial reflecting sounds or reverberation sounds is carried out based on this assumption. Thus, as long as the input audio signal can be regarded as a signal from a single sound source, the conventional sound field addition apparatus can perform optimum sound field addition processing without any particular preliminary processing such as separation, enhancement and suppression of the input audio signal. However, when many sound sources also exist outside of the stage, the sound field control based on the above assumption cannot provide satisfactory results.
More specifically, even if sounds recorded at a plurality of sound fields (places) are contained in the input audio signal, the conventional sound processing apparatus performs identical sound processing on these sounds from the different sound sources contained in the input audio signal so that the resulting output sound is not necessarily natural.
When, for example, on-the-spot broadcast speech sound and ambient sound from the audience are mixed in the input signal as in a live sports broadcasting, addition of a hall sound field should be performed only on the ambient sound. However, the conventional sound processing apparatus adds reflecting and reverberation sounds not only to the ambient sound but also to the broadcast speech sound so that the reproduced speech sound becomes extremely unnatural like so-called public address system speech. Further, when an interval change is performed by the conventional apparatus, the interval of the ambient sound is changed together with that of the on-the-spot broadcast speech sound, resulting in a very uncomfortable reproduced sound.